1. Technical Field
The present invention relates to the field of introducer assemblies for providing percutaneous access to the vascular system. More specifically, the invention relates to a low profile apparatus suitable for introducing catheters and other interventional devices into the vascular system with a minimal amount of trauma to the patient.
2. Background Information
Many medical procedures require the percutaneous placement of an interventional medical device, such as a catheter, into an artery or vein. Such interventional devices may be used for, among other things, blood pressure monitoring, blood sampling, and the administration of fluids and medicaments to a patient.
Typically, such devices are introduced into the vascular system using the well-known Seldinger percutaneous entry technique. In the Seldinger technique, the physician makes an oblique entry into the artery or vein with a beveled needle. A wire guide is passed through the bore of the needle into the artery or vein. The needle is thereafter withdrawn, leaving the wire guide in place. The catheter or other interventional device is then passed over the wire guide, through the puncture, and into the artery or vein at the needle puncture site. Once the catheter is in place, the wire guide can be withdrawn.
One of the disadvantages of this procedure is that the initial needle stick must normally be made with a needle that is large enough to accept the wire guide through its central bore. Conventional wire guides often comprise a tightly wound helical stainless steel wire coil. In order to have sufficient rigidity to properly support and lead many standard catheters and other interventional devices in common use in modern medicine, such wire guides are typically constructed to have an outer diameter in the range of about 0.035 to 0.038 inch (0.89 or 0.97 mm). This diameter of wire guide will typically pass through an 18 gauge thinwall needle. An 18 gauge needle typically has a 0.050 inch (1.27 mm) outer diameter (O.D.) and a 0.042 inch (1.07 mm) inner diameter (I.D.).
The 18 gauge needle is the most common sized needle used for initial vascular access, and has become a standard needle for use with the Seldinger technique for percutaneous catheterization. However, the O.D. of an 18 gauge needle is just large enough to damage tissue or cause excessive bleeding if it does not enter the vessel correctly, or if it inadvertently penetrates an organ or other unintended body structure. As a result, it is desirable to utilize a smaller gauge needle, such as a 21 gauge thinwall needle, for initial entry. A 21 gauge thinwall needle typically has a 0.032 inch (0.81 mm) O.D. and a 0.022 inch (0.56 mm) I.D., or smaller. Needles of 21 gauge thinwall, or smaller, are considered small enough that they do not damage tissue or organs, or cause excessive bleeding if inserted off target. In addition, smaller gauge needles generally have correspondingly shorter bevels at the needle tip compared to the size of the bevel tip of an 18 gauge needle. Thus, it is much easier to get a short bevel into the lumen of a small vessel than the longer bevel of the 18 gauge needle.
Unfortunately, the bore of a needle of 21 gauge, or smaller, is not large enough to enable a standard 0.035 inch or 0.038 inch (0.89 mm or 0.97 mm) diameter wire guide to be passed therethrough. The largest wire guide that can be easily introduced into such small gauge needles is normally a wire of 0.018 inch (0.46 mm) O.D. However, many diagnostic and interventional devices need at least a 0.035 inch (0.89 mm), and more preferably a 0.038 inch (0.97 mm), diameter wire guide to provide sufficient support to enable the physician to optimally introduce and manipulate the device through the vasculature over the wire. Thus, unless a larger diameter wire guide is introduced into the vasculature, many such devices cannot be successfully introduced.
U.S. Pat. No. 4,650,472 describes an apparatus which enables a physician to introduce a medical device, such as a catheter, into the body of a patient by making the initial puncture with a small gauge needle, such as a 22 gauge (0.028 inch; 0.72 mm O.D.) needle, in place of the larger conventional 18 gauge needle. The '472 patent is incorporated by reference herein. A 0.018 inch (0.46 mm) outer diameter wire guide is initially inserted through the bore of the small gauge (e.g. 22 gauge) needle. The needle is thereafter withdrawn, and a removable inner cannula, or dilator, is provided over the wire guide but inside an outer sleeve portion of the catheterization apparatus. This removable inner cannula has a tapered tip, and provides a transition between the large distal opening of the outer sleeve and the 0.018 inch wire guide. The inner cannula is generally about 0.038 inch (0.97 mm) O.D., and the outer sleeve is sized to fit over the inner cannula.
The outer sleeve and the inner cannula of the apparatus disclosed in the '472 patent are normally inserted into the blood vessel in tandem. The diametrical transition of the leading end of this tandem is intended to minimize the trauma that may otherwise be caused by the insertion of a large diameter outer sleeve over a small diameter wire guide. Once the outer sleeve is properly positioned within the blood vessel, the inner cannula and the smaller wire guide can be withdrawn, leaving the outer sleeve in place. A larger (0.035 to 0.038 inch) (0.89 to 0.97 mm) wire guide can then be introduced through the outer sleeve and into the vessel. If desired, the outer sleeve can thereafter be removed from the patient, leaving the larger wire guide in the vessel ready to accept a catheter or other interventional device. The apparatus of the '472 patent has been successfully used to percutaneously insert a medical device, such as a catheter, having a large outer diameter into a blood vessel when the initial insertion is made with an introducer needle and a wire guide which are much smaller in diameter than the distal opening of the catheter.
The apparatus of the '472 patent thus enables the physician to introduce larger diagnostic and interventional devices into a vessel than would otherwise be possible in a procedure in which initial vessel entry has been made with a small gauge needle. When the apparatus is inserted into the vessel as described, however, the physician must exert sufficient force to overcome the resistance provided at the “bump” that is present at the transition between the distal end of the outer sleeve and the underlying portion of the inner cannula. If this force is not carefully controlled, the physician may inadvertently exert too great a force to overcome the bump, and thereby puncture the side of the vessel opposite the initial stick. Thus, although the device of the '472 patent may be successfully used to introduce large devices when initial entry is made with a small gauge needle, it is nonetheless desired to further improve this device, by providing a design which reduces the amount of force required to insert the outer sleeve into the vessel, and thereby reduces the possibility of an inadvertent puncture of the opposing vessel wall.